It is generally known in engineering to use heat to fuse toner images, applied to a substrate using an electrophotographic printing unit, for example. When fusing heat, the toner is heated to above its glass temperature, i.e. melted, resulting in a close bond with the substrate. Furthermore, during heating it is possible that there will be a cross-linking of the toner particles, which increases the stability of the toner image in particular against heat effects.
A known fusing unit, as generally used for toner applications, has a heatable fusing roller and a pressure roller between which a fusing gap is formed for passing through of a substrate. To extend the fusing gap in the transport direction of the substrate and hence enlarge a contact surface between the substrate and the fusing roller, the pressure roller usually has an elastic surface which is compressed in the area of the fusing gap. At high fusing speeds, there is however the risk with a fusing unit of this type that substrate faults like substrate bucklings will occur in the area of the fusing gap, or that the substrate will wrap around the fusing roller. To prevent both this and the adhesion of toner particles to the fusing roller, it is know how to use separating oil on the fusing roller, which however can lead to other problems.
Furthermore, a fusing unit of this type must have a sufficient distance from the printing unit that it does not grip a substrate until it is completely removed from the printing unit, since the gripping of the substrate might otherwise impair the printing process. In particular, it is even usual to grip a substrate with the fusing unit of the above type only when the substrate has been completely released by the transporting mechanism that transports the substrate during toner application. This is intended to prevent the substrate firmly gripped by the rollers from disturbing an even movement of the transporting mechanism. This results in considerable space requirements for printing devices of this type.